Seawater pressure-driven desalinization method using a gravity-driven brine return

ABSTRACT

A method of removing salt from seawater to produce potable freshwater. Apparatus that may be used with the method includes a large metal cylinder, with open top and bottom ends, anchored to the sea floor offshore. Several pressure hulls may be attached to the side of the cylinder. Within each pressure hull there are several reverse osmosis devices (“RODs”), each containing a membrane that will allow water molecules, but not sodium and chlorine ions, to pass through. Due to the pressure differential, freshwater passes through the membranes by reverse osmosis, and is pumped out of the pressure hulls to a storage facility onshore. After equilibrium is reached, the pumps for the brine can be turned off, as gravity will cause brine to flow down from the pressure hulls through an opening in the bottom of the cylinder. Alternatively, a reverse osmosis system may be supported on an elevated undersea platform.

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application is a Divisional Application of Utility patentapplication Ser. No. 10/036,433, filed Jan. 7, 2002, which was aDivisional Application of Utility patent application Ser. No.09/716,230, filed Nov. 21, 2000, which was a Continuation-In-Part ofUtility patent application Ser. No. 09/287,658, filed Apr. 7, 1999.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a reverse osmosis method ofremoving the salt from water in the ocean or inland bodies of saltwater, using the pressure of the seawater itself, and the force ofgravity.

[0004] 2. Description of the Prior Art

[0005] Due to the shortage of freshwater in the southwestern UnitedStates and other arid parts of the world, there have been numerousinventions for desalinating sea water, by reverse osmosis, distillation,and other means. However, desalinization remains an expensive process.The concentrated brine produced as a by-product of desalinization canitself contribute to pollution of the environment in onshore facilities.The production of electricity or other forms of energy consumed indesalinization can also contribute to pollution of the air, water andland.

[0006] U.S. Pat. No. 3,171,808, issued on Mar. 2, 1965, to Henry W.Todd, discloses an apparatus for extracting fresh water from ocean saltwater, using vanes that are not included in the present invention.

[0007] U.S. Pat. No. 3,456,802, issued on Jul. 22, 1969, to Marc Cole,discloses an apparatus for desalinization by submerged reverse osmosis,without the gravity-driven brine return of the present invention.

[0008] U.S. Pat. No. 4,125,463, issued on Nov. 14, 1978, to James W.Chenoweth, discloses a reverse osmosis desalinization apparatus andmethod, that is placed in a well hole for desalinating salty groundwater.

[0009] U.S. Pat. No. 4,189,379, issued on Feb. 19, 1980, to Warren T.Finley, discloses a method of bringing nutrient-rich water from theaphotic zone of the ocean to the photic zone.

[0010] U.S. Pat. No. 4,335,576, issued on Jun. 22, 1982, to Harold H.Hopfe, discloses a device for producing freshwater from seawater whichfloats on the surface of the sea. It derives the energy fordesalinization from the motion of the waves on the surface of the water.Movement of the water on the surface causes reaction plates to move, andthe movement is ultimately transmitted to pistons that move in cylindersto exert pressure on seawater to force reverse osmosis.

[0011] U.S. Pat. No. 4,452,969, issued on Jun. 5, 1984, to FernandLopez, discloses a reverse osmosis apparatus for producing freshwaterfrom seawater, which is designed to be temporarily submerged, as on afishing line. U.S. Pat. No. 4,770,775, issued on Sep. 13, 1988, toFernand Lopez, discloses another apparatus for the production offreshwater from seawater, which is also designed to be temporarilysubmerged, and has a chamber that expands as freshwater is produced.Both of these apparatuses use the pressure of the seawater itself toforce reverse osmosis.

[0012] U.S. Pat. No. 5,167,786, issued on Dec. 1, 1992, to William J.Eberle, discloses a wave power collection apparatus, which is anchoredin the sea floor, and in one embodiment desalinates seawater by reverseosmosis. The movement of floats is used in that embodiment to turn agenerator which produces electricity to power pumps that force seawaterthrough a membrane in a reverse osmosis unit.

[0013] U.S. Pat. No. 5,229,005, issued on Jul. 20, 1993, to Yu-Si Fokand Sushil K. Gupta, discloses a process for the desalinization ofseawater, by lowering reverse osmosis devices into the ocean by means oflines attached to pulleys, and raising them again by the same means toremove the freshwater produced. The pressure of the seawater itself isused to force reverse osmosis of the seawater across a membrane toproduce freshwater.

[0014] U.S. Pat. No. 5,366,635, issued on Nov. 22, 1994, to Larry O.Watkins, discloses a desalinization apparatus and means in which aseparator is placed on the sea floor, and the pressure at the sea flooris used to force seawater through a membrane to form freshwater byreverse osmosis, which is then pumped out.

[0015] U.S. Pat. No. 5,914,041, issued on Jun. 22, 1999, to Dennis H.Chancellor, discloses channel based reverse osmosis, in which reverseosmosis units are placed within a deep channel. The channel containsunpurified liquid (such as salt water) at a level such that the pressureacross the membranes of the reverse osmosis units causes purified liquid(such as fresh water) to accumulate in cavities in the reverse osmosisunits, from which it is emptied and pumped to the surface.

[0016] U.S. Pat. No. 5,916,441, issued on Jun. 29, 1999, to Roger J.Raether, discloses an apparatus for desalinating salt water in a mineshaft.

[0017] U.S. Pat. No. 5,944,999, issued on Aug. 31, 1999, to Dennis H.Chancellor, Marc Chancellor and Jacquetta M. Vogel, discloses a modularfiltration system, in which the weight of the fluid being filtered isused to drive the filtration process.

[0018] British Patent No. 2,068,774, published on Aug. 19, 1981, to JoseLuis Ramo Mesple, discloses an apparatus for desalinating water byreverse osmosis in cells located deep underground, utilizing thepressure resulting from the water being deep underground.

[0019] Japanese Patent No. 55-99379, published on Jul. 29, 1980, toFujii Riichi, discloses a deep sea reverse osmotic pressuredesalinization method, in which a permeable membrane module is installedin the deep sea bottom and a vent pipe is mounted to it.

[0020] Japanese Patent No. 55-155788, published on Dec. 4, 1980, toNitto Kako K K, discloses a desalinization method with reverse osmosismodules sunk to a specific depth in the sea, in which fresh wateraccumulates in a water well and is pumped out.

[0021]The Osmotic Pump, by Octave Levenspiel and Noel de Nevers,Science, January 1974, Volume 183, Number 4121, pages 157-160, disclosesthe idea of using the weight of sea water to drive a desalinizationprocess, but does not disclose the structures and mechanisms of thepresent invention.

[0022] The present invention is distinguishable from the prior artcited, in that only it takes advantage of the fact that the concentratedbrine produced as a by-product of reverse osmosis desalinization isheavier than seawater to reduce the energy consumed in desalinization,by means of a gravity-driven brine return. None of the above inventionsand patents, taken either singly or in combination, will be seen todescribe the present invention as claimed.

SUMMARY OF THE INVENTION

[0023] The present invention is an apparatus and method of removing saltfrom seawater to produce potable freshwater. In the first threepreferred embodiments, a large metal cylinder, with open top and bottomends, is anchored to the floor of the ocean (or inland sea) offshore.Several pressure hulls are attached to the side of the cylinder. Theinterior of each pressure hull is maintained at about one atmosphere ofpressure, but the hulls are submerged at a depth at which the ambientwater pressure is several atmospheres. Within each pressure hull thereare several reverse osmosis devices (RODs), each containing a membranethat will allow water molecules, but not sodium and chlorine ions, topass through. Check valves allow sea water to pass from outside thehulls into the RODs. Due to the pressure differential, water moleculespass through the membranes by reverse osmosis, while salt is leftbehind, and freshwater is pumped out of the pressure hulls to a storagefacility on shore (or where ever else it is needed). Initially, theseawater remaining on the other side of the membrane, which has agreatly increased concentration of salt due to water passing through themembrane, is pumped into the cylinder. (The water with an increasedconcentration of salt is hereinafter referred to as brine.) After aninitial surge, the level of the brine in the cylinder will eventuallyreach equilibrium, at a height below the height of the seawater outsidethe cylinder, due to the greater weight of the brine compared tounconcentrated seawater. After equilibrium is reached, the pumps for thebrine can be turned off, as gravity will cause it to flow down from thepressure hulls through an opening near the bottom of the cylinder. Thiswill reduce the energy needed to desalinate seawater. (It will still benecessary to pump out the freshwater.)

[0024] In the fourth preferred embodiment, a reverse osmosis systemcontaining one or more RODs is supported by a platform on the sea floor,and there is no cylinder. In the fifth preferred embodiment, thecylinder is supported by a flotation device, and the reverse osmosissystem is retained on the cylinder. In both the fourth and fifthembodiments, an elongated brine return runs downhill on the sea floor.

[0025] Accordingly, it is a principal object of the invention to providea means for reducing the energy required to desalinate seawater.Conventional desalinization plants, located on or near the seashore,require four pumping processes: first, pumping the seawater to theplant; second, pumping to raise the pressure high enough for the RODs tooperate; third, pumping the brine back out to sea; and fourth, pumpingthe freshwater to a reservoir or a treatment facility for furtherpurification, and ultimately to the consumer. The present inventioneliminates all but the fourth pumping process. While prior inventions ofoffshore desalinization apparatus, as in U.S. Pat. No. 5,366,635 toWatkins, will also eliminate the first and second processes, only theinstant invention will also eliminate the third process of pumping outthe brine, without requiring that energy be expended in raising theRODs, as in U.S. Pat. No. 4,452,969 to Lopez and U.S. Pat. No. 5,229,005to Fok et al.

[0026] It is second object of the invention to provide a means forreducing the need for using expensive real estate on or near theoceanfront for desalinization facilities. As no oceanfront ornear-oceanfront property is used exclusively for the process, most realestate costs associated with desalinization plants can be avoided. Someoffshore site leasing may be required, but this cost should be muchlower than for offshore sites involved in petroleum or mineralextraction.

[0027] It is a third object of the invention to provide a means formaking the expansion of desalinization facilities easier and lessexpensive. As each platform must have a clear navigation zone around it(as most jurisdictions require by law), sufficient space for attachingadditional pressure hulls to the cylinder will be available and facilityexpansion considerably eased. The expansion of a facility is limitedonly by the number of pressure hulls that can be fitted onto thecylinder at appropriate depths, rather than allowances made by a zoningcommission with many other constituents to satisfy, as may the case witha land-based desalinization facility.

[0028] It is a fourth object of the invention is to provide a means forreducing the cost of desalinizing seawater by centralizing maintenancefacilities, as the pressure hulls can be removed and taken to a centralfacility for maintenance, rather than the on-site maintenance requiredby conventional shore-based desalinization plants.

[0029] It is a fifth object of the invention to reduce pollution of theshoreline from the release of concentrated brine by desalinizationplants. Conventional onshore desalinization facilities pump their brineout to sea through a bottom-laid pipeline, which releases the brine onor near the ocean floor. Releasing the brine near the ocean floorincreases the area affected by the brine's toxicity. Existing methods toreduce the toxic effects add to the cost of desalinization throughgreater plant infrastructure requirements or reduced process efficiency.The present invention allows an offshore desalinization facility torelease its brine into mid-water, where mixing with the ocean current ismore efficient, with fewer effects upon bottom-dwelling flora and fauna.Because the facility can be located offshore, ocean currents and tidalaction will thoroughly mix the brine back into the surrounding seawater,and the overall impact of increased salinity from the brine releasecould be infinitesimal as little as two or three kilometersdown-current.

[0030] It is an object of the invention to provide improved elements andarrangements thereof in an apparatus for the purposes described which iscost effective, dependable and fully effective in accomplishing itsintended purposes.

[0031] These and other objects of the present invention will becomereadily apparent upon further review of the following specification anddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0032]FIG. 1 is a schematic environmental front elevational view of thefirst preferred embodiment of the invention.

[0033]FIG. 2 is a schematic environmental front elevational view of thesecond preferred embodiment of the invention.

[0034]FIG. 3 is a schematic environmental front elevational view of thethird preferred embodiment of the invention.

[0035]FIG. 4 is a schematic cross-sectional view of one of the pressurehulls of the first type that may be used in any of the first threepreferred embodiments of the invention.

[0036]FIG. 5 is a schematic cross-sectional view of one of the pressurehulls of the second type that may be used in any of the first threepreferred embodiments of the invention.

[0037]FIG. 6 is a schematic environmental front elevational view of thefourth preferred embodiment of the invention.

[0038]FIG. 7 is a schematic environmental front elevational view of thefifth preferred embodiment of the invention.

[0039] Similar reference characters denote corresponding featuresconsistently throughout the attached drawings.

DETAILED DESCRIPTION OF THE P REFERRED EMBODIMENTS

[0040] The present invention is an apparatus and method of removing saltfrom seawater to produce potable fresh water. It may be used in eitherthe oceans or in inland bodies of salt water.

[0041]FIG. 1 is a schematic environmental front elevational view of thefirst preferred embodiment of the invention. A large metal cylinder 10,with an open top end 12 and an bottom opening 14, rests on platform 13which is anchored to the floor A of the ocean B (or inland sea)offshore. (Alternatively, a tube or channel of a different shape and/orwith a plurality of top openings and/or a plurality of bottom openingsmay be used. Also, the apparatus can be supported by flotation devices,or by cables attached to ships, rather than resting on the sea floor.)Bottom pressure hulls 15 are removably attached to the side of thecylinder, above or below the equilibrium level C of brine in thecylinder. When greater production capacity is needed, upper pressurehulls 16 are added.

[0042]FIG. 2 is a schematic environmental front elevational view of thesecond preferred embodiment of the invention, which is the same as thefirst preferred embodiment, except that the bottom of the cylinder restsdirectly on the sea floor.

[0043]FIG. 3 is a schematic environmental front elevational view of thethird preferred embodiment of the invention, which is the same as thesecond preferred embodiment, except that brine pipe 35 projects over acliff E in the sea floor. This embodiment may be used in areas such asthe Red Sea where the submarine topography makes it possible. Sendingthe brine over a submarine cliff will make possible more efficientmixing of the brine with the sea water.

[0044]FIG. 4 is a schematic cross-sectional view of one of the pressurehulls of the first type that may be used in any of the preferredembodiments of the invention. The fresh water enclosure 18 in theinterior of each pressure hull is maintained at a pressure below that ofthe ambient seawater, preferably at one atmosphere of pressure, but thehulls are preferably submerged at a depth at which the ambient waterpressure is several atmospheres. Within each pressure hull there areseveral reverse osmosis devices 20 (“RODs”), each having a selectivelypermeable membrane 22 surrounding a brine enclosure 24. The membraneallows water molecules, but not sodium and chlorine ions, to passthrough. (Other substances may also be filtered out of the seawater,depending on the characteristics of the membrane.) The pressure hullshave an external skin 26 which is impermeable to water. Seawaterconduits 28, having check valves 30, pass through the external skin andthe membranes, to allow seawater to pass from outside the hulls into theRODs. The check valves enhance the efficiency of the process, bypreventing brine from returning directly to the surrounding seawater bythe same route. The space between the external skin and the othercontents of the pressure hulls forms the fresh water enclosure 18. Dueto the pressure difference, water molecules pass through the membranesby reverse osmosis, and desalinated water is pumped out of the pressurehulls through the freshwater conduit 32 and (referring back to FIG. 1)pipeline 34 to an onshore storage facility 36 (or where ever else it isneeded). The freshwater conduit should be external to the cylinder, asconcentrated brine is highly corrosive. Freshwater pumps (not shown inthe drawings) may be located in the storage facility, the pipeline, thecylinder, and/or elsewhere. The pumping out of the freshwater maintainsthe pressure difference across the membrane, so that reverse osmosis cancontinue. The desalinated water may undergo further purification at alocal water treatment plant.

[0045]FIG. 5 is a schematic cross-sectional view of one of the pressurehulls of the second type that may be used in any of the preferredembodiments of the invention. It differs from the first type in having adry interior 42, which is kept dry by an air vent 44 to the atmosphereabove the surface D through which any moisture evaporates. The RODs areenclosed by water proof surfaces 46. Freshwater is drained from the RODsby freshwater pipes 48 which are connected to the fresh water conduit32.

[0046] Initially, the seawater remaining on the other side of themembranes (“brine”), which has a greatly increased concentration of saltdue to water passing through the membranes, is pumped into the cylinderby the brine pumps 38 through the brine conduits 40 (see FIG. 4). Atleast one of the brine pumps is preferably located in each pressurehull, as shown, but other locations are possible. The pumping out of thebrine maintains a pressure difference across the seawater conduits,causing seawater to continue to flow into the reverse osmosis devices.After an initial surge, the level of the brine C in the cylinder willeventually reach equilibrium at an elevation below the sea level Doutside the cylinder (see FIG. 1), due to the greater weight of thebrine compared to unconcentrated seawater. After equilibrium is reachedthe pumps for the brine can be turned off, as gravity will cause it toflow down from the hulls through the bottom opening 14 of the cylinder.This will reduce the energy needed to desalinate seawater. (It willstill be necessary to pump out the freshwater.) The lower pressure hulls15 should be attached to the cylinder first, as the pressure differencewill be greatest at lower depths. When greater capacity is needed, theupper hulls 16 should be added, but desalinization will not be asefficient in them, as the pressure difference will be lower.

[0047] The earth's gravity will cause the brine in the tube to flow outof the bottom opening until the weight of the brine in the tube equalsthe weight of an equivalent column of water in the sea outside the tube.As brine continually flows into the tube when the invention is inoperation, the weight of the brine in the tube will continue to beheavier than that an equivalent column of seawater outside, and brinewill continue to flow out. If there were no currents in the sea, thesalinity of the sea in the immediate area around the tube couldeventually rise to almost the degree of salinity in the tube (though notto complete equality, due to diffusion of salt through the seawater).This would cause the level of brine in the tube to rise to almost thelevel of the sea outside the tube, and it would be necessary toreactivate the brine pumps for desalinization to continue. (This mightactually happen in inland bodies of salt water, which lack drainage tothe oceans, if desalinization were carried out on a massive scale over along period of time.) Thus, the present invention derives its energysavings, not out of nothing, as would a perpetual motion machine, butfrom the force of the earth's gravity, from ocean currents andinterlayer mixing that are driven by electromagnetic radiation producedby nuclear reactions in the sun, and from diffusion made possible byrandom movements of molecules and ions in the seawater that are alsodriven by heat from the sun.

[0048]FIG. 6 is a schematic environmental front elevational view of thefourth preferred embodiment of the invention, in which a single reverseosmosis system 50 is elevated above the sea floor F by a platform 52.The reverse osmosis system has an external skin and contains on or moreRODs (not shown in FIG. 6) which are constructed as described above. Aseawater inlet (not shown in FIG. 6) allows water to pass into thereverse osmosis system after passing through a screen for fish and largematter, a pre-filter for silt and particulate matter, a micro-filter forbacteria and suspended solids, and a check valve. Desalinated water isremoved from the fresh water enclosures of the RODs through a freshwater return 54 by at least one fresh water pump (not shown in FIG. 6)which may be located in the reverse osmosis system, along the freshwater return, or on shore. Water having an increased concentration ofsalt is removed from the brine enclosures of the RODs through a brinereturn 56. As shown in FIG. 6, the brine return passes down theplatform, over the sea floor, and has an outlet 58 where the brine isreleased into the surrounding seawater, preferably at a considerabledistance (as indicated by the pair of jagged lines) from the reverseosmosis system (so that the brine does not soon become mixed back inwith the seawater being desalinated) and over an undersea cliff G orother area of the sea floor having a lower elevation the sea floor onwhich the platform rests. The reverse osmosis system is located farenough below the surface of the sea H that the weight of the overlyingsea water creates sufficient pressure for reverse osmosis to occuracross the membranes in the RODs. A pressure differential is maintainedacross the membranes by the fresh water pumps. Initially, the brine ispumped out of the brine enclosures by a brine pump (not shown in FIG. 6)until the brine return is filled (or charged) with brine. Then the brinepump can be turned off, while the inlet 60 of the brine return remainsopen, and the brine will continue to flow downhill through the brinereturn under the force of gravity, because it is heavier than thesurrounding seawater. This saves the energy that would otherwise beneeded to pump out the brine. (Note that the weight of the brine in thebrine return, and the drop in depth from the brine return's inlet to itsoutlet, must be great enough that the downward pressure of the brineunder the force of gravity exceeds the back pressure across themembranes in the RODs that is maintained by the fresh water pump.)

[0049]FIG. 7 is a schematic environmental front elevational view of thefifth preferred embodiment of the invention, which is similar to thefourth preferred embodiment, except that rather than being supported bya platform on the floor, it is supported by a flotation device 62 on thesurface of the sea. A channel 64, which is preferably a hollow verticalcylinder with an open top 66 and a closed bottom 68, is retained on theflotation device, and the reverse osmosis system 50 is retained on thechannel below the flotation device. The top of the channel passes abovethe surface of the sea. The reverse osmosis system is held in place bylines 70 connected to anchors 72 in the sea floor. Rather than beingpumped directly into the brine return, brine is pumped into the channelthrough an outlet (not shown in FIG. 7) of the brine enclosures. Theinlet of the brine return is connected to the channel, so that brine canthen flow from the channel into the brine return. Once both the channeland the brine return are filled with brine, the brine pump can be turnedoff, while the outlet of the brine enclosures remains open, and brinewill continue to flow out through the brine return, as in the fourthpreferred embodiment. Because the brine is denser than the surroundingseawater, the surface of the brine in the channel will be below thesurface of the sea, and it will have an increased pressure gradient(i.e., the pressure of the brine will increase more rapidly over ashorter vertical distance than the pressure of the seawater). This hasthe consequence that the channel can (and should) be positioned inrelation to the reverse osmosis systems in such a manner that thepressure in the channel is less than the pressure in the brineenclosures in the RODs, thus causing the brine to flow out from the RODsinto the channel, and from the channel out through the brine return.

[0050] It is to be understood that the present invention is not limitedto the embodiments described above, but encompasses any and allembodiments within the scope of the following claims.

I claim:
 1. A method of desalinating seawater, comprising the steps of:allowing seawater to pass through an inlet with a check valve into abrine enclosure; reverse osmosis of the seawater as water molecules passfrom the brine enclosure through a membrane into a fresh waterenclosure, while the membrane blocks the passage of sodium and chlorineions; maintaining a pressure differential across the membrane by pumpingdesalinated water out of the fresh water enclosure; and pumping waterhaving an increased concentration of salt out of the brine enclosure toa brine return; whereby, if the pumping is discontinued after the brinereturn is filled with the water having an increased concentration ofsalt, the force of gravity will cause the water having an increasedconcentration of salt to continue to flow through the brine return. 2.The method of desalinating seawater according to claim 1, wherein thebrine enclosure is directly connected to an inlet of the brine return.3. The method of desalinating seawater according to claim 1, whereinthere is a channel having at least one top opening, the brine enclosurehas an outlet connected to the channel through which water having anincreased concentration of salt is pumped from the brine enclosure intothe channel, and an inlet of the brine return is connected to thechannel.
 4. The method of desalinating seawater according to claim 3,wherein the channel has at least one bottom opening.
 5. The method ofdesalinating seawater according to claim 4, wherein the channel iscylindrical.
 6. The method of desalinating seawater according to claim5, wherein at least one pressure hull is retained on the channel, saidpressure hull having an external skin that is impermeable to water. 7.The method of desalinating seawater according to claim 6, wherein saidpressure hull contains at least one reverse osmosis device.
 8. Themethod of desalinating seawater according to claim 7, wherein saidreverse osmosis device contains said membrane, said fresh waterenclosure, and said brine enclosure.
 9. The method of desalinatingseawater according to claim 8, wherein the channel rests directly on thebottom of the sea.
 10. The method of desalinating seawater according toclaim 8, wherein the channel is supported by a platform that rests onthe bottom of the sea.
 11. The method of desalinating seawater accordingto claim 8, wherein the inlet has a screen and at least one filterthrough which seawater must pass before it reaches the membrane.
 12. Amethod of desalinating seawater, comprising the steps of: allowingseawater to pass through an inlet with a check valve into a brineenclosure; reverse osmosis of the seawater as water molecules pass fromthe brine enclosure through a membrane into a fresh water enclosure,while the membrane blocks the passage of sodium and chlorine ions;maintaining a pressure differential across the membrane by pumpingdesalinated water out of the fresh water enclosure; and pumping waterhaving an increased concentration of salt out of the brine enclosure toa brine return that is an elongated channel that passes along the seafloor, from an area where the sea floor has a higher elevation near aninlet of the brine return, to an area where the sea floor has a lowerelevation near an outlet of the brine return; whereby, if the pumping isdiscontinued after the brine return is filled with the water having anincreased concentration of salt, the force of gravity will cause thewater having an increased concentration of salt to continue to flowthrough the brine return.
 13. The method of desalinating seawateraccording to claim 12, wherein the brine enclosure is directly connectedto an inlet of the brine return.
 14. The method of desalinating seawateraccording to claim 12, wherein the membrane, the fresh water enclosureand the brine enclosure, are contained within a reverse osmosis systemthat is supported by a platform that rests on the bottom of the sea. 15.The method of desalinating seawater according to claim 12, wherein thereis a channel having at least one top opening, the brine enclosure has anoutlet connected to the channel through which water having an increasedconcentration of salt is pumped from the brine enclosure into thechannel, and an inlet of the brine return is connected to the channel.16. The method of desalinating seawater according to claim 15, whereinthe channel is supported by a floatation device.
 17. The method ofdesalinating seawater according to claim 16, wherein the membrane, thefresh water enclosure and the brine enclosure, are contained within atleast one reverse osmosis device within a reverse osmosis system that isretained on the channel.
 18. The method of desalinating seawateraccording to claim 17, wherein the reverse osmosis system is held inplace by lines anchored to the sea floor.
 19. The method of desalinatingseawater according to claim 18, wherein the channel has a closed bottom.20. The method of desalinating seawater according to claim 12, whereinthe inlet has a screen and at least one filter through which seawatermust pass before it reaches the membrane.